The Universal Serial Bus was originally developed in 1995 by a consortium of companies. The major goal of USB was to define an external expansion bus, which makes adding peripherals to a PC as easy as hooking up a telephone to a walljack. The ease-of-use and low cost made USB successful in the marketplace, with most peripheral vendors around the globe developing products to its specification.
One role of system software is to provide a uniform view of the system for all applications software. The system software may be adapted to hide hardware implementation details so that application software is more portable. The system software may manage the dynamic attach and detach of peripherals. This phase, called enumeration, involves communicating with the peripheral to discover the identity of a device driver that it should load, if not already loaded. A unique address is assigned to each peripheral during enumeration to be used for run-time data transfers. During run-time the host PC initiates transactions to specific peripherals, and each peripheral accepts its transactions and responds accordingly. Additionally, the host PC software incorporates the peripheral into the system power management scheme and may manage overall system power without user interaction.
The hub may provide additional connectivity for USB peripherals and managed power to attached peripherals. The hub may recognize dynamic attachment of a peripheral and provide device power for peripheral operation. A newly attached hub may be assigned its unique address, and hubs may be cascaded up to five levels deep, for example. During run-time a hub may operate as a bidirectional repeater and may repeat USB signals as required on upstream cables towards the host and downstream cables towards the device.
The USB peripherals may be adapted to request transactions sent from the host PC. The peripheral may respond to control transactions that, for example, request detailed information about the device and its configuration. The peripheral may transmit and receive data to/from the host using a standard USB data format. This standardized data movement to/from the PC host and interpretation by the peripheral gives USB enormous flexibility with little PC host software changes. The USB 1.1 peripherals may operate at 12 Mb/s or 1.5 Mb/s.
USB 2.0 is an evolution of the USB 1.1 specification, providing a higher performance interface. The USB 1.1 connectors and full-speed cables may support the higher speeds of USB 2.0 without any changes. The higher transmission speed may be negotiated on a device-by-device basis and if the higher speed is not supported by a peripheral, then the link operates at a lower speed of 12 Mb/s or 1.5 Mb/s as determined by the peripheral. The external USB 2.0 hub may have different signaling rates on its ports. Using a 40× multiplier for USB 2.0, the USB 2.0 hub may have an input rate of 480 Mb/s and output rates of 480 Mb/s, for example, for attached high speed USB 2.0 peripherals, and 12 Mb/s or 1.5 Mb/s, for example, for attached USB 1.1 peripherals. The USB 2.0 hub may match the data rates sent out of its downstream ports to the data rate appropriate to the attached device. The higher data rate of USB 2.0 may open up the possibilities of new peripherals, for example, video-conferencing cameras may perform better with access to higher bandwidth.
The system software may comprehend the increased capabilities of USB 2.0 peripherals so that it can optimize performance and detect sub-optimal configurations, for example, a USB 2.0 peripheral attached to a USB 1.1 hub, and recommends a better configuration for attaching the peripherals. A USB 2.0 hub may be adapted to accept high-speed transactions at the faster frame rate and deliver them to high-speed USB 2.0 peripherals and USB 1.1 peripherals. This data rate matching responsibility may require increased hub complexity and temporary buffering of the incoming high-speed data. In the case of communicating with an attached USB 2.0 peripheral, the hub repeats the high speed signals on appropriate USB 2.0 upstream and downstream cables. This allows USB 2.0 peripherals to utilize the majority of USB 2.0 bandwidth.
To communicate with USB 1.1 peripherals, a USB 2.0 hub may comprise a mechanism that supports the concept of matching the data rate with the capabilities of the downstream device. The hub may be adapted to manage the transition of the data rate from the high speed of the host controller to the lower speed of a USB 1.1 device.
A USB device may be serviced by a local USB host controller and appropriate host software to configure, operate, monitor and manage the USB devices. However, in order to enable a host with limited local intelligence to support some USB devices, the USB processing may be executed in a remote location based on a local entity sending the signals to that remote location. For example, in a client/server setup, where the client is a smart terminal with limited local processing but would like to offer the flexibility of supporting peripherals, for example, USB 1.1 peripherals such as keyboard, mouse and printer.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.